Sunan an-Nasa'i, Volume 2, Book 13, Hadith 1255 (DarusSalam) ⓘ

It was narrated that 'Abdullah said: "The Prophet prayed Zuhr with five rak'ahs, and it was said to him: 'Has something been added to the prayer?' He said: 'Why are you asking?' They said: 'You prayed five.' So he turned around and prostrated twice."

أَخْبَرَنَا مُحَمَّدُ بْنُ الْمُثَنَّى، وَمُحَمَّدُ بْنُ بَشَّارٍ، - وَاللَّفْظُ لاِبْنِ الْمُثَنَّى - قَالاَ حَدَّثَنَا يَحْيَى، عَنْ شُعْبَةَ، عَنِ الْحَكَمِ، عَنْ إِبْرَاهِيمَ، عَنْ عَلْقَمَةَ، عَنْ عَبْدِ اللَّهِ، قَالَ صَلَّى النَّبِيُّ صلى الله عليه وسلم الظُّهْرَ خَمْسًا فَقِيلَ لَهُ أَزِيدَ فِي الصَّلاَةِ قَالَ ‏ "‏ وَمَا ذَاكَ ‏" ‏ ‏.‏ قَالُوا صَلَّيْتَ خَمْسًا ‏.‏ فَثَنَى رِجْلَهُ وَسَجَدَ سَجْدَتَيْنِ ‏.‏